Research On Technical Measures For Preventing Debris Flow Impact Of Railway Piers

With the development of China’s economic construction,especially the implementation of "the Western Development" and "the Belt and Road" national strategy,China has built more and more railways in the western mountainous areas.Debris flow is a common mountainous geological disaster,so railways encounter with mudslides will be inevitable.However,due to the traffic conditions in the mountainous area,a large number of bridges need to be built to meet the traffic requirements of the road.Although the railway bridge piers are thicker than the highway bridge piers,they may also be damaged or even destroyed in the debris flow disaster,causing a lot of economic losses and casualties.Therefore,it is necessary to install a suitable protective device to reduce the impact of debris flow on railway piers.First,several important parameters of debris flow were introduced,and then CFD,fluid-structure coupling,and important multiphase flow models and turbulence models in Fluent were introduced which were used in subsequent simulations.Then,in Fluent,the fluid part of the impact of the debris flow on the unprotected bridge pier was simulated,and the fluid-solid coupling analysis was completed in Ansys-workbench to analyze the force of the bridge pier and the flow field of the debris flow.Furthermore,the same simulation method was used to analyze the piers with non-contact tripod-shaped three-pile protection and contact cone-shaped fluid protection,and compare the results obtained from the previous non-protected piers.After comprehensive evaluation,the most reasonable layout situation was obtained.Finally,the impact of different initial velocities,severity and viscosity of debris flows on the selected bridge piers with the best protection devices was simulated,and their protective effects on different debris flows was analyzed.In the end,the following conclusions were reached:(1)For the tripod-shaped three-pile protection,shortening the distance between the piles and the distance to the bridge pier will improve the protection effect.The influence of the height of the pile varies with the distance between the pile and the pier.After comprehensive analysis,under the tripod-shaped three-pile protection device with the best shape,the ratio of the impact force on the pier of the protection device to the peak overturning moment without protection is 0.76 and 0.73,respectively,which has a significant decrease.(2)For cone-shaped fluid protection,the protection effect is best when the protection device is greater than the depth of the debris flow inlet.In the case of different angles of attack,the best one is the angle of attack of 40°.After comprehensive analysis,the ratio of the impact force on the bridge pier to the peak overturning moment without protection is0.36 and 0.19 under the optimal cone-shaped fluid diversion protection device,which is compared with the previous tripod-shaped three-pile protection device.There has been a significant decline.(3)The best non-contact tripod-shaped three-pile protection and contact cone-shaped fluid protection have almost no difference in the protection effects of debris flows with different inlet flow speed and different density and viscosity.